Modern consumer electronics products such television receivers, video cassette recorders (VCRs) and video disk players typically include so called "on-screen" display ("OSD") provisions for displaying status information and instructions in the form of textual (alphanumeric) and pictorial graphics on the screen of a display device which is normally used to display video information. Early OSD systems were only capable of displaying a limited amount of status information, such as the channel or program number of the program currently being viewed and the current time. Later OSD systems were capable of displaying instructional information for guiding a user in making adjustments such as setting the contrast and brightness of a television receiver or setting the recording times and channel numbers of programs to be recorded in the future by a VCR.
In a typical OSD system, the OSD graphics information is stored in a memory in what is known as a "bit-mapped" form. A "bit-map" is a rectangular array of picture elements ("pixels") which defines the shape of the graphics to be displayed. Each memory location of the bit-map memory contains a code word for a respective graphics pixel. The code word defines the intensity level or color of the graphics pixel. For textual information, each of the code words may simply comprise a single bit designating the presence (e.g., by logic "1" level) or the absence (e.g., by logic "0" level) of a pixel with a particular intensity level (e.g., white) or color. For pictorial graphics, each of the code words may represent any one of a plurality of colors. For example, a four-bit code word can represent 16 (24) different colors. The color information for each pixel is stored in a memory called a "color palette", and the code words are used to address the color palette memory. In other words, the color palette memory is used as a "look-up" table for the colors of the graphics pixels.
Some very recent OSD system are capable of displaying very sophisticated graphics including limited animated graphics. Animation, involves the sequencing of graphical information in such a way as to produce the effect of motion. The known technique for providing OSD animation in a consumer product involves storing a series of bit-mapped graphical images and reading individual ones of the stored bit-mapped graphic images out of the memory in the appropriate sequence, usually under microprocessor control. Depending on the size of the display area being animated, the amount of memory required to store the series of bit-mapped graphic images may be very substantial. In addition, the microprocessor workload required to read-out and manipulate the bit-mapped graphic images is very high. The memory and microprocessor requirements can make a high quality animation feature very expensive, especially for use in consumer products
In the article "A New Architecture for a TV Graphics Animation Module", IEEE Transactions on Consumer Electronics, 39(1993), No. 4 (November), the authors describe a TV graphics animation player/edit system using a workstation which can receive an analog video signal, and a digital signal representing graphicaldata. Real time compression is applied to both, and they arc stored in a disk memory. Data is then read from the disk memory, decompressed in real time, and displayed on a monitor.
European patent publication O 597 616, published May 18, 1994, discloses a system for mixing animation sequences with computer graphics information, also for display on a computer display screen. The animation sequences are stored in compressed format. The compressed animation sequences are then retrieved from storage, decompressed, synchronized with the computer graphics information and sent to a computer monitor.
European patent publication O 660 609, published Jun. 28, 1995, discloses a system in which the MPEG encoding method is used to encode an I frame with a background image, and various P frames, each encoding the chances to the background image I frame necessary to make a menu or other user window-like control, such as a drop-down list or button. These frames are transmitted from a central location, such as a cable head end, to a receiver location to provide a user with a graphical interface to interact with the central location.
European patent publication O 601 647, published Jun. 15, 1994, discloses a system in which video data is stored in an internal format. Input encoders receive video signals in various formats, and convert the video signal from that format to the internal format. Output decoders retreive internal format video data and convert it to respective output formats. A multiplexer couples one of the output decoders to the display device.